Along with recent widespread of data communication networks, so-called home networks allowing communications between household electric appliances, computers and other peripheral apparatuses connected to the network are prevailing also in homes. The home network provides users with convenience and comfort, such as sharing a data processing function between apparatuses connected to the network and transmitting and receiving content to and from the apparatuses, and is predicted to become more common.
On the other hand, however, it is required to consider a countermeasure against illegal accesses in the network of this type. A device in a home network, such as a server, often stores content requiring copyright management, including private content and paid content.
Content and secret information stored in the server in a home network have a possibility of being illegally acquired, for example, by an external access via the Internet. If such an illegal access is allowed, secret is leaked and there arises a severe problem in terms of management of the content copyright.
When content requiring copyright management such as movies and music is transmitted via a network, the content transmission range is limited to a range in which the usage is permitted, for example, only among devices in a home network. However, recent widespread of the Internet poses a problem of illegal content transmission via the Internet.
Under the Copyright Law of Japan, digital content as one of literary works is protected from illegal use such as copying and falsification without permission. Article 30 of the Copyright Law of Japan stipulates that it shall be permissible for a user to copy by himself a work for the purpose of his personal use, family use or other similar uses, without limiting the kind of a work and a type of copying. Article 49, Paragraph (1) of the Copyright Law of Japan also stipulates that if a copy made for the purpose of personal use is used for other purposes, reproduction right of the author is transferred, and prohibits so-called uses of copies for other purposes.
In these days of active uses of digital content, many technologies have been developed to protect copyright. For example, Digital Transmission Content Protection (DTCP), which is the industry standards or digital transmission content protection, defines a mechanism for transmitting content whose copyright is protected. For example, refer to a non-patent document 1 [DTCP Specification Volume 1 Version 1.3 (Informational Version).
The DTCP defines digital content transmission on a home network using IEEE 1394 and the like as a transmission line. It is presumed that content transmission via a home network is of personal use or family use as stipulated in the Copyright Law of Japan. The DTCP defines an authentication protocol between devices during content transmission and a transmission protocol of encrypted content.
Namely, a server as a content provider performs authentication with a client as a content receiver, and encrypts a transmission channel by using a key shared during the authentication procedure, and transmits content. By using the DTCP, content can therefore be transmitted under protection. Since the client cannot acquire an encryption key unless authentication with the server succeeds, the client cannot enjoy the content. [Non-patent document 1] DTCP Specification Volume 1 Version 1.3 (Informational Version).